In recent years, portable electronic devices have been introduced which can perform the functions of both a calculator and a timepiece, some of these devices being designed to be worn on the wrist. Due to the small size of such devices, it is only possible to utilize a battery of relatively small size and capacity as a power source. It is therefore necessary to ensure that the power dissipation of the device shall be as low as possible.
Until now, the input circuit of the keyboard of such a portable electronic device, used to produce electrical signals to indicate that a key has been depressed and to identify the particular key, have been of similar design to the keyboard input circuits used in electronic calculators of conventional design. Such a type of circuit dissipates a relatively high level of power, and is not suitable for a device in which power consumption must be reduced to the lowest practicable degree. The above remarks are also applicable to the input circuits of external actuation members such as control switches, utilized to select the display of time information or calculation information, for example. Such input circuits must suppress spurious switch bounce pulses generated when switch contacts are closed.